The NAVSTAR global positioning system (GPS) and other global navigational satellite systems (GNSS) provide accurate and reliable navigation signals around the globe. GPS receivers work well whenever a clear view of the sky is available. Indoors or near obstructions, however, GPS receivers may be limited by weak signals, reflections and multipath interference. Thus alternative or supplementary navigation systems are needed for indoor use.
Domed stadiums, shopping malls and warehouses all provide examples of situations in which indoor navigation systems may be helpful to people trying to find their way. An indoor navigation system based on radio frequency identification (RFID) tags was disclosed in “Reverse RFID location system” by G. Best et al., U.S. Ser. No. 12/544,869 filed on 20 Aug. 2009. In a reverse RFID (R-RFID) navigation system a set of RFID tags are placed in known locations, e.g. distributed inside a building. Each RFID tag stores its position. A user of the R-RFID system estimates his position based on the positions reported by nearby RFID tags. For example a user may be located such that his RFID tag reader can interrogate three nearby RFID tags. The user may estimate his position as the average of the three reported positions.
R-RFID techniques are a promising new indoor navigation solution. However, RFID readers are specialized devices; not everyone has one. What is needed is an indoor navigation system that almost anyone can use.